

Focus and Klar are basically the same, except for the telemetry. Iirc Klar was created because having telemetry would possibly run afoul of some German data privacy laws.
Klar would be the pick of the two. You could also use a different fork that you used like focus where you set it to only use private browsing and delete data/cookies etc on quit.
Yes, that should be it. Firefox runs its own version of SafeBrowsing, but it falls back to Google if it sees something that is not in its database. Then it sends a hash to Google to check it.